I could see that. I'm _only_ using it for personal so I haven't really run into the issues that you're talking about.
I think for Dropbox to operate in a pure filesystem-native-first experience they're probably approaching it from the 1 computer = 1 person standpoint (or one logged in user on the computer at least).
I've got one colleague who mistakenly let Dropbox psuedo-merge his personal and business accounts several years ago. He still hasn't completely fixed it!
I was around when they introduced the "multi account" support, and it was very easy to see how/why they did it. Instead of updating their clients to support multiple accounts (which they should have done), the client just keeps supporting only one account. Then on their back end they return "merged" content to the client. You can easily see how this can create chaos, because other people can also be updating your personal and business content, and untangling it all is a mess.
I think for Dropbox to operate in a pure filesystem-native-first experience they're probably approaching it from the 1 computer = 1 person standpoint (or one logged in user on the computer at least).